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Airflow under a cowling

Thinking of aero air-cooled engines and specifically cooling airflow. Why did everyone settle for an airflow that goes through and then is deflected 90deg down versus straight through and out through the sides say?

To enable better cooling cylinders behind #1 and #2. Otherwise, I can’t imagine cooling 6-cylinder engine.

LDZA LDVA, Croatia

The flat-four or flat-six configuration needs a buildup of pressure above (or below, but AFAIK nobody does that) which forces air (vertically) through the cylinder fins, presumably.

Usually #1 and #2 get good air, #5 and #6 (the rear ones) get good air too because it gets bunched up at the back, and #3 and #4 get the least, which reflects in the CHTs.

You need very good baffles and baffle seals for this to work.

Administrator
Shoreham EGKA, United Kingdom

Forcing the air through the fins I understand – but why up-down vs front-to-back? Pressure build-up would be the same if exhaust holes are properly sized.

I guess I am missing something basic here, but to me it always seemed logical to have the flow of cooling air going rearward and upward, exiting the cowling near the windshield, the air can then follow the natural way of warmer air going upwards, cooler air downwards. Not much of an issue in flight, probably, where ram pressure will be a much more important factor, but quite relevant during taxi and even more when running stationary?

PS if I may once more refer to my own situation, which is a bit different from most participants’: for this once I am on the “better” side with my mixed cooling Rotax 912 – no concerns about shock cooling and never been too warm, not even close – in fact my only temperature issue is to get the oil to heat up sufficiently – even in summer I have 60% of the oil radiator taped off, and the oil temp rarely gets higher than the indicated minimum of 90 degrees C.

But some fellows with Jabiru engines have or have had trouble and to spare, getting their baffles to work efficiently enough.

Last Edited by at 02 Oct 10:39
EBZH Kiewit, Belgium

Here is a more advanced aero engine cooling system, something coming from the future.

That looks great however it would take away all the fun of having a potential USD xx.xxx engine overhaul bill at the back of your mind every time you touch the throttle / mixture.

Thinking of aero air-cooled engines and specifically cooling airflow. Why did everyone settle for an airflow that goes through and then is deflected 90deg down versus straight through and out through the sides say?

Everyone did not settle for this. There are many other configurations flying. But there are other considerations also. Best configuration in case of fire. Best configuration in case of an oil/fuel leak. Best practical configuration for maintenance and so on. All things considered, the “standard” option works best for a flat 4/6.

What are the “many other configurations” actually flying?

What are the “many other configurations” actually flying?

There are inline air cooled engines. Intake in the front/side, exhaust through the side. There are several flat 4/6 with exhaust on the side. The Panthera for instance and many VW configurations also, almost all motorgliders with Limbacs (at least those I know of). Aircraft with aft mounted engines have of course a different configuration.

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